Upper Delaware reservoir drawdown begins June 1 to fix major leakage of aqueduct

After a year's delay, a long-planned drawdown of the New York City reservoirs feeding the Upper Delaware River is scheduled to start June 1, in advance of a closure of the Delaware Aqueduct to repair massive leaks from the tunnel beneath the Hudson River.

Of application to Pennsylvania and New York residents along the Upper Delaware is the prospect of a major rainstorm making these reservoirs spill, without the aqueduct in service to divert excess water to the city's water system. The drawdown is hoped to create sufficient space in the reservoirs, coupled with regular river releases, to mitigate the possibility.

The Upper Delaware Council (UDC), which has kept close tabs on the project, received an update at its May 2 meeting in Narrowsburg, New York. Jennifer Garigliano, director of Water Resources Management with the NYC Department of Environmental Protection (NYCDEP) said that the shutdown is scheduled for Oct. 1, 2024, to May 2025. Everything, however, is weather dependent.

"This is the largest and most complex repair project in the history of the water supply," Garigliano said. "There are so many moving parts and pieces that have to all align to get this done right."

The project has been postponed twice in the past two years due to more work that was required. This will be the first shutdown and draining of the aqueduct since 1957-1958.

Water from the Cannonsville Reservoir on the West Branch of the Delaware above Hancock, New York, and the Pepacton Reservoir on the East Branch as well as the Neversink Reservoir, funnels down to the Rondout Reservoir where it is channeled into a single, 85-mile aqueduct to NYC. It is the longest tunnel in the world. The Delaware, Catskill and Croton watersheds supply over a billion gallons of drinking water daily to 10 million residents in NYC and 70 communities to the north.

Normally this aqueduct carries about half of this water, Garigliano said. Once the three Delaware reservoirs are shut down, the city will rely 100% on the Catskill and Croton reservoirs.

To stop the long-standing leakage where the tunnel bores beneath the Hudson, a 2.5-mile bypass tunnel has been built 600 feet under the river. To connect it to the aqueduct at Newburgh and Wappinger on either side of the Hudson and make the repairs, the aqueduct must be shut down. The roughly $1 billion project has been studied and planned for over 20 years, the NYCDEP states.

NYCDEP reports that leaks waste an estimated 20 million gallons daily, about 95% of it escaping the tunnel through a leak near Newburgh west of the Hudson.

Once the aqueduct is closed, the only means to reduce the Delaware reservoir levels will be through releases to the Upper Delaware River. Depending on rainfall, the level of the Delaware reservoirs will be lowered by 30% or more, Garigliano noted. This will leave significant voids, meant to capture rainfall, and lessen the chance for spillage over the dams and flowing down the Upper Delaware.

Deluges from storms in the mid-2000s created significant spilling and flooding, even with the aqueduct online to take water.

Normal reservoir releases regulated by the Flexible Flow Management Program are to continue. These help to attenuate flood risk and drought, as well as help downstream fisheries and support the river recreation industry. The program was first adopted in 2007-2008 and was revised in 2017.

The project timeline can be overthrown by changing hydrologic conditions. The best information available from long-term weather prediction services will be used. If a bailout is called during the shutdown, it can take one to nine weeks to return the aqueduct to service.

Garigliano said that contractors will start mobilizing in July to be ready to go on Oct. 1 when they close the aqueduct. It will take a few weeks to depressurize and drain the aqueduct so workers can enter. The plan is to finish by May 2025, prior to June 1 when the reservoirs need to be full for the summer season when water demand is highest.

"This is such a large and complex project, if something does happen or does not go according to schedule and we don't think we're going to finish by June 1, we will get the aqueduct back to a point where we can turn it back on," Garigliano said.

Virginia Dudko, UDC chairperson, asked what the "worst case scenario" would be.

"There are so many things that could go wrong in a project of this size," Garigliano replied, noting a lot of risk analysis has been done. "We have so many people, so many hands on; everybody's watching it. Once this starts there will be daily meetings... to run through where they are, what's happening that day, who is responsible for what, where they stand in the timeline, and if something should go wrong, what would happen. That coordination will happen daily."

Garigliano said the goal is to maintain flood mitigation releases and maintain the needed reservoir voids.

The UDC meets on the first Thursday of the month at 7 p.m., at 211 Bridge St., Narrowsburg, New York.

For more information on the Delaware Aqueduct project, visit nyc.gov/site/dep/whats-new/delaware-aqueduct-shutdown-impact-upstate.page.

Peter Becker has worked at the Tri-County Independent or its predecessor publications since 1994. Reach him at pbecker@tricountyindependent.com or 570-253-3055 ext. 1588.